Under the Gemological Institute of America (GIA) certification system, cut grading is quite straightforward. The depth percentage and table percentage are the two main factors that have an impact on the cut grade. The depth percentage is worked out by dividing the depth by the average girdle diameter. The table percentage is calculated by dividing the measurement of the longest table by the average girdle diameter. You ought to do these calculations in millimeters.
The GIA ranks the cut of a diamond from Excellent or Ideal to Poor. Other grades in between include Very Good, Good, and Fair. Needless to say, the labels make this grade very easy to understand. You should stay away from cuts that are Poor or Fair because it indicates that the diamond has been cut too shallow or too deep and, therefore, the light will escape. The light will reflect beautifully if you go for a Very Good or Ideal cut. To the untrained eye, the difference between these two cuts can be very difficult to spot. A Good Cut is an option worth considering, as it is affordable yet quality is not compromised too much. You will still get a beautiful sparkle, yet you do need to be mindful that a small amount of light will escape.